1. Field of the Invention
This invention relates to retreading method and machinery for fabricating a recapped tire by cutting a vulcanized tread material, vulcanized in form of a continuous belt, such that leading and trailing edges to be bonded meet in tread pattern, and then winding the tread strip on a base tire.
2. Description of the Related Art
In a pre-curing method (cold recapping method), which winds on a base tire a vulcanized tread (pre-cured tread) strip having a pattern formed on its surface, then bonds its leading and trailing edges, and vulcanizes the tire in a vulcanization chamber, the vulcanized tread strip is previously vulcanized and molded in a length corresponding to the length of one to three tires, and this tread material is cut and wound on a prepared base tire, followed by bonding its leading and trailing edges.
Typically used for this bonding is a technique that wraps the circumferential surface of a base tire with a tread rubber material approximately up to 340 degrees, loosely putting the remainder of the tread rubber material on the base tire to find a position meeting the leading edge, where the remainder part of the tread rubber material should be cut, then marks that position and cut it there with a cutter, and bonds the resultant trailing edge of the tread rubber material in abutment with the leading edge.
This method, however, could not provide a high productivity because it relies on operator's visual detection of the position of the tread rubber to be cut before bonding the leading and trailing edges and on operator's manual task of cutting it with a cutter.
Furthermore, although this method cuts out a strip from a tread material to meet with the length of the outer circumference of a base tire, base tires have various circumferential lengths depending on differences in growth amount of the outer diameter, differences in outer diameter among different patterns of tire manufacturers, and so on.
Thus the cut position is not constant relative to the surface pattern, and divided pattern blocks come out with various sizes.
For example, assume that a tread material 01 having a tread pattern as shown in FIG. 10 is to be cut at the cut position C-C′.
When a particular pattern block B is remarked, one divisional pattern block b at one side of the cut position C-C′ has a larger volume whereas the other divisional pattern block b′ has an extremely small volume.
If a divisional pattern block with such an extremely small volume remains on a recap after being molded, the recap is liable to suffer local wearing, during use, at the portion of the divisional pattern block b′ bonded with a small length of bonding as shown in FIG. 11 showing an example of joint of the leading and trailing edge.
In some cases, a groove and a block portion may come to butt at the joint of the leading and trailing edges of the tread rubber material, which will make a defective joint and will lead to local separation of the joint.
Furthermore, unless divisional pattern blocks of the leading edge and the trailing edge do not meet well, there occur size differences in blocks at the joint of the leading and trailing edges, and this may cause local wearing, or, if a pattern groove or a thin filleted block end abuts with the cut surface of a pattern block, separation of the joint will occur due to the defective bonding, and the outer aspect of the pattern will be damaged.
To cope with these problems, there is a method of ensuring pattern matching at the joint between the leading and trailing edges by preparing a tread rubber material having a leading edge and a trailing edge cut along a line having the same pattern as the cut line of the leading edge and distant from the leading edge by a length nearest to the required length, and putting the tread rubber material on the base tire while expanding or contracting it to adjust its length with the circumferential length of the base tire.
This conventional method, however, burdens operators with various tasks upon cutting the tread rubber material at a desired pattern position. That is, an operator must stop the machine to confirm the cut position by lightly pressing a cutter on the tread rubber material, or estimate the cut position from the anvil position of the cutter; if the cut position is not a proper position, the operator must move the tread rubber material to a proper position by manually operating a conveyor or other transport machine; and he or she actually cuts it after a gain confirming the cut position.
As reviewed above, since the but position is visually confirmed by an operator and manually adjusted in position, high accuracy of the cutting position cannot be expected even at the cost of the required time and labor.
While winding the tread rubber material on the base tire, when the operator winds the last part of the tread rubber material after finishing the winding of a larger half of the tread rubber, the operator must expand or contract the last part of the tread rubber material to adjust the length such that the trailing edge comes into exact abutment with the leading edge.
Therefore, the cutting task is inefficient, and the finishing quality of the winding job is largely affected by the skill of the operator.
Further, since the tension or compression is locally concentrated to the trailing end portion of the tread rubber material, the tread rubber material cannot be wound on the base tire in a uniform condition.